Point light source for a laser scanning microscope and process for feeding at least two different laser beams of different wavelengths into a laser scanning microscope

ABSTRACT

A point light source is disclosed for a laser scanning microscope ( 7 ). At least two lasers ( 1  and/or  2  and/or  3; 4 ) with different wavelengths may be coupled in the microscope ( 7 ). To combine the advantages of a multiline laser with those of the use of several independent one-line lasers, the point light source is characterised by at least two laser light sources the beam of which are fed into a beam combiner ( 5 ), and by an optical fibre ( 6 ) which leads directly or indirectly from the beam combiner ( 5 ) to the microscope ( 7 ).

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority of German patent applications DE-A-19614 929.0 and DE-A-196 33 185.4.

1. Field of the Invention

Point light source for a laser scanning microscope and process forcoupling at least two lasers of different wavelength into a laserscanning microscope

The invention relates to a point light source for a laser scanningmicroscope, it being possible to couple at least two lasers of differentwavelengths into the microscope. The invention further relates to aprocess for coupling at least two lasers of different wavelength into alaser scanning microscope.

2. Background of the Invention

Light sources of the type under discussion here are required in laserscanning microscopes, in particular in the case of confocal microscopy.In this case, what principally matters is, within the context of amulticolor application, to couple laser light of different wavelengthinto the microscope. This has to take place with quite particularconsideration being given to the adjustability of the laser and withconsideration being given to the stability of the adjustment.

From practice, two different arrangements are known for multicolorapplication in laser scanning microscopes. Within the context of a firstalternative, a laser (ArKr) having a plurality of simultaneouswavelengths is used. In this case, it is inherent in the system that inthat instance all laser lines—per se—are adjusted to one another. Inthis case, the selection of the wavelengths as well as the setting ofthe power is accomplished by an AOTF (Acousto Optical Tunable Filter).Consequently, each laser line may be set, independently of the others,in its power continuously even down to very low powers. The coupling intakes place in each instance through a single mode fiber. The advantageof the above possibility of coupling in resides in a compact scanner, inabsolute adjustability as well as in decoupling of the vibration causedby the laser cooling.

SUMMARY OF THE INVENTION

The advantages described hereinabove do however also involve quiteconsiderable disadvantages. An ArKr laser covers—as has already beenmentioned above—a plurality of laser lines simultaneously. As these aregenerated in a resonator, this always brings about an instability of theindividual lines, particularly as, in the laser, only the total power iskept constant by a regulating system. Depending upon the setting of thetotal power, the noise occurring in this case may amount to up to 10percent “peak to peak” and thus reduces the image quality with respectto the signal/noise ratio. In contrast to this, single-line lasersachieve noise of only just 1 percent.

Furthermore, in the event of failure of the—singular —laser the systemis entirely incapable of functioning. The available laser lines are inall cases dependent upon the laser-active gas and the mixing thereof. Asthis alters over the service life of the laser, an impairment of alllaser lines takes place in the course of time. Finally, only the laserlines of the gas mixture employed are available, so that in this casethere is always a restriction-on selection.

In the case of a system which is further known from practice, in allinstances a plurality of lasers are coupled directly into a laserscanning microscope. In the event of a laser fault, only one laser linefails. In correspondence with the function of these lasers, the otherlaser lines remain available. By reason of the single line operation,the laser power exhibits high stability. Single-line lasers have alonger service life than lasers having a plurality of wavelengths. Foreach laser line, the laser power may be optimally coordinated with theexperimental conditions without further auxiliary measures.

It is also the case that the abovementioned coupling of a plurality oflasers into a laser scanning microscope exhibits considerabledisadvantages, since, specifically, the laser beams from the differentlasers have to be focused or adjusted onto one and the same point inprecisely the same direction. In this case, there are four degrees offreedom per laser. If the focusing or adjustment does not take place toa sufficient extent, the images recorded using the different laser linesare not in register. However, the analysis of images which are inregister is precisely the purpose of a multiple excitation of the typeunder discussion here.

A further disadvantage of the use of a plurality of different lasers isto be seen in that conventional beam combining arrangements andadjustment systems have to be readjusted frequently. This procedure isextremely complicated, since in the conventional arrangements thevarious degrees of freedom of the adjustments are not sufficientlydecoupled from one another.

Thus, an alteration of angle always also leads to an alteration ofposition. Consequently, the adjustment target is attained only aftermany adjustment cycles, so that the adjustment can scarcely be carriedout by the user himself. A particular service provided by themanufacturer of the equipment is accordingly absolutely necessary.Finally, a plurality of lasers together are always more costly than asingle laser having a plurality of wavelengths.

Now, the object of the invention is to specify a point light source fora laser scanning microscope, which light source makes use of theadvantages of the two abovementioned systems—multiline laser and aplurality of single-line lasers—and at least to a very great extenteliminates the disadvantages thereof. Furthermore, the intention is tospecify a process for using such a point light source.

The point light source according to the invention achieves the aboveobject by, a point light source for a laser scanning microscope whichcomprises at least two laser light sources which couple into a beamcombiner and an optical fiber leading indirectly or directly from thebeam combiner to the microscope.

According to the invention, it has been recognized in this case that theuse of at least two independent laser light sources and thus of at leasttwo different lasers involves the advantages which have been discussedhereinabove. The associated disadvantages may—likewise according to theinvention—be eliminated in that, even before coupling into the laserscanning microscope, a beam combination takes place, so that from thereonward mutually adjusted laser beams or laser lines having a pluralityof wavelengths—in the sense of a multiline laser—are available, which isso in the case of a laser having a plurality of simultaneously occurringwavelengths.

After the beam combination, the combined laser lines are guidedsimultaneously via an optical fiber to the microscope and are coupled inthere—as in the case of a laser having a plurality of simultaneouslyoccurring wavelengths. Consequently, from the beam combination into thefiber onward, all laser lines are automatically adjusted to one another.Accordingly, an adjustment or setting takes place exclusively in thebeam combiner, which may be realized in the form of a compact component.A particular adjustment to the coupling in of the laser scanningmicroscope is not necessary in any circumstances.

In a particularly advantageous manner and to minimize the expenditure ondesign or apparatus, in particular also for the optimal use of theavailable space, one of the lasers couples directly into the beamcombiner. In other words, this laser is directly allocated to the beamcombiner. At least one further laser is coupled into the beam combinervia an optical fiber; in this case, a single mode fiber may be involved.Besides the laser coupling directly into the beam combiner, specificallyand in a quite particularly advantageous manner two or three furtherlasers may in each instance couple into the beam combiner via a separateoptical fiber. In this case, laser lines having different wavelengthsmay be coupled in, so that the result is a multicolor application.

The beam combiner may comprise a conventional component known from theprior art or an appropriate arrangement. Thus, the beam combiner couldbe designed as a dichroic beam combiner with splitter mirrors ofdiffering transmission/reflection characteristics. Any selectablearrangement for beam combination is useable in each instance; in thiscase, a monolithic arrangement is to be preferred for reasons ofstability, precision, simpler production, but also for reasons of asmaller space requirement. Exchangeability of the beam combiner forgeometrically similar but physically differently “trimmed” devices forbeam combination is feasible.

In a quite particularly advantageous manner, the beam combiner isdisposed in a housing. The laser coupling directly into the beamcombiner is possibly fixed to the housing via a particular adapter heador couples directly into the beam combiner at the housing via theadapter head. The further lasers couple in each instance via an opticalfiber into the housing, and thus into the beam combiner disposed in thelatter and the beam path thereof.

The housing is preferably made of metal. Production from plasticmaterial is of advantage particularly in circumstances in which thehousing may be manufactured by injection molding.

For the selection and individual setting of the line power, in a furtheradvantageous manner an AOTF (Acousto Optical Tunable Filter) isconnected downstream of the beam combiner. To obtain a compact module,this AOTF is likewise disposed within the housing. With the aid of theAOTF, it is also possible inter alia to compensate any possiblecoupling-in losses.

There may further be connected downstream of the beam combiner an AOM(Acousto Optical Modulator), which serves for beam modulation and rapidbeam deenergization. In this case also, the arrangement within thehousing is advisable, particularly since this makes it possible torealize a compact module as a whole.

Finally, with respect to the point light source of the presentinvention, it is of quite particular advantage if the optical fiberleading from the beam combiner to the microscope, i.e. the fibercoupler, is designed as a single mode fiber. As a result of this, it isachieved that smaller disadjustments become effective, merely as aresult of low losses on coupling into the fiber. As has already beenmentioned previously, these low losses on coupling-in and thusassociated changes in the line power conditions may be compensated bythe use of an AOTF.

The inventive process for coupling at least two lasers of differentwavelength into a laser scanning microscope achieves the initiallymentioned object by a process defined in that the lasers are coupled injointly as a singular point light source with simultaneous wavelengthsor laser lines that are coupled jointly as a singular point lightsource, into the microscope.

In this case, it is of quite particular advantage if a beam combinationtakes place already prior to coupling into the microscope—in anindependent component. From there, coupling into the microscope thentakes place via an optical fiber which is preferably designed as asingle mode fiber.

Within the context of the process described here, one of the laserscould be coupled directly and at least one further laser could becoupled via an optical fiber into the encased component—beam combiner.Prior to coupling into the microscope, a selection and individualsetting of the line power could take place by means of an AOTF (AcoustoOptical Tunable Filter).

Likewise, prior to coupling into the microscope, a beam modulation andpossibly rapid beam deenergization could be possible by means of an AOM(Acousto Optical Modulator). Both options may be provided for the sakeof a compact design of the point light source or of the point lightmodule within the housing.

There are now various possibilities for refining and further developingthe teaching of the present invention in an advantageous manner. In thisconnection, reference is to be made to the explanation, which follows,of an illustrative embodiment of the invention with reference to thedrawing.

BRIEF DESCRIPTION OF THE DRAWING

In conjunction with the explanation of the preferred illustrativeembodiment of the invention, refinements and further developments of theteaching which are in general preferred are also explained. In thedrawing:

The single FIGURE shows a diagrammatic representation of a point lightsource according to the invention having a total of four lasers.

DETAILED DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENTS

The module represented in the single FIG. may be defined in total as apoint light source for a laser scanning microscope or for a confocalmicroscope; in this case, in total four lasers 1, 2, 3, 4 are providedhere. The lasers 1, 2, 3, 4 have different wavelengths.

According to the invention, a beam combiner 5 is provided, into whichthe lasers 1, 2, 3, 4 couple in their laser beams. The “opticalcoupling” of all lasers 1, 2, 3, 4 to a downstream AOTF (Acousto OpticalTunable Filter) 11 takes place exclusively via the lower splitter mirrorof the beam combiner 5. From the beam combiner 5, a common beam pathleads through the AOTF 11 and an AOM (Acousto Optical Modulator) 13 viaan optical fiber 6 to the laser scanning microscope 7 of which only anindication is given in the figure.

The single figure shows particularly clearly that one of the lasers,namely the laser identified by the reference symbol 4, couples directlyinto the beam combiner 5. The other lasers 1, 2 and 3 couple in eachinstance into the beam combiner 5 via an optical fiber 8.

The beam combiner 5 is disposed in a housing 9. In correspondingfashion, the laser 4 which couples directly into the beam combiner 5 isdirectly connected to the housing 9. A corresponding adapter head hasnot been shown here, for the sake of simplicity.

The further lasers 1, 2 and 3 lead via the optical fibers 8 through thehousing wall, or through corresponding connections 10, into the interiorof the housing; in this case, coupling into the beam combiner takesplace there.

As has already been mentioned hereinabove, according to the single FIG.an AOTF (Acousto Optical Tunable Filter) 11 is connected downstream ofthe beam combiner 5 within the housing 9; in this case, this AOTF 11serves for the selection and individual setting of the line power.Downstream of the AOTF 11 there is in turn connected an AOM (AcoustoOptical Modulator) 13 which serves for beam modulation and rapid beamdeenergization. From there, the optical fiber 6 designed as a singlemode fiber leads via a corresponding connection 12 to the laser scanningmicroscope 7, in order there to couple in the laser beam having aplurality of wavelengths or a plurality of laser lines in the sense of apoint light source.

With respect to the process according to the invention, reference ismade to the general part of the description in order to avoidrepetitions.

Finally, it should be quite particularly pointed out that theillustrative embodiment discussed hereinabove serves merely for thediscussion of the teaching claimed here, but does not restrict thelatter to the illustrative embodiment.

PARTS LIST

1 Laser

2 Laser

3 Laser

4 Laser

5 Beam combiner

6 Optical fiber (from the beam combiner to the laser scanningmicroscope)

7 Laser scanning microscope, microscope

8 Optical fiber (from the laser to the beam combiner)

9 Housing

10 Connection (into the housing)

11 AOTF

12 Connection (to the laser scanning microscope)

13 AOM

What is claimed is:
 1. A microscope comprising: a connector on amicroscope for a first optical fiber; and a point light source for themicroscope, in which at least two lasers of different wavelengths arecoupled into the microscope which further comprises at least two laserlight sources which couple into a beam combiner, wherein at least one ofthe lasers is coupled via a second optical fiber into the beam combiner,and wherein the first optical fiber optically couples laser light fromthe beam combiner to the microscope.
 2. The microscope as claimed inclaim 1, wherein one of the lasers couples directly into the beamcombiner and two further lasers couple in each instance via the secondand a third optical fiber into the beam combiner.
 3. The microscope asclaimed in claim 1, wherein one of the lasers couples directly into thebeam combiner and three further lasers couple in each instance via thesecond, a third, and a fourth optical fiber into the beam combiner. 4.The microscope as claimed in claim 1, wherein the beam combiner designedas a dichroic beam combiner.
 5. The microscope as claimed in claim 1,wherein the beam combiner is disposed in a housing, and wherein one ofthe lasers is coupled directly into the beam combiner and is fixed tothe housing via an adapter head.
 6. The microscope as claimed in claim5, wherein the housing is made of metal.
 7. The microscope as claimed inclaim 5, wherein the housing is made of plastic material.
 8. Themicroscope as claimed in claim 5, further comprising: an AOTF (AcoustoOptical Tunable Filter) for the selection and individual setting of theline power disposed within the housing, downstream of the beam combinerto receive a combined light beam.
 9. The microscope as claimed in claim5, further comprising: an AOM (Acousto Optical Modulator) for beammodulation and rapid beam deenergization disposed within the housing,downstream of the beam combiner to receive a combined light beam. 10.The point light source as claimed in claim 1, wherein the second opticalfiber leading from the beam combiner to the microscope is a single modefiber.
 11. A process for coupling at least two lasers of differentwavelengths into a microscope, the process comprises the steps of:combining the at least two lasers in an encased housing; and couplingthe at least two lasers into the microscope jointly as a singular pointlight source.
 12. The process as claimed in clam 11, wherein, from theencased housing, coupling into the microscope takes place via a singlemode optical fiber.
 13. The process as claimed in claim 12, Wherein oneof the at least two lasers couples directly and at least one furtherlaser couples via an optical fibre into the encased housing.
 14. Theprocess as claimed in claim 12, wherein, prior to coupling into themicroscope, a selection and individual setting of the line power takesplace by an AOTF (Acousto Optical Tunable Filter).
 15. The process asclaimed in claim 12, wherein, prior to coupling into the microscope, abeam modulation and rapid beam deenergization takes place by an AOM(Acousto Optical Modulator).
 16. The microscope as claimed in claim 1,wherein the microscope is a laser scanning microscope.
 17. Anarrangement for a laser scanning microscope, comprising: a port disposedon a microscope to receive a first optical fiber; a first laser emittinga first light beam having a first wavelength; a second laser emitting asecond light beam having a second wavelength, the second wavelengthdifferent from the first wavelength; a beam combiner to combine thefirst and second light beams; and a second optical fiber to couple thefirst light beam into the beam combiner, wherein the first optical fibercouples light output from the beam combiner into the port of themicroscope.
 18. The point light source according to claim 17, furthercomprising: a housing to encase the beam combiner, wherein the beamcombiner includes a dichroic mirror, and wherein a path of the secondlight beam from the second laser to the first optical fiber defines anoptical path, wherein the beam combiner combines the first and secondlight beams along the optical path; and an AOTF (Acousto Optical TunableFilter) disposed along the optical path between the beam combiner andthe second optical fiber.
 19. The point light source according to claim18, further comprising: an AOM (Acousto Optical Modulator) disposedalong the optical path between the AOTF and the second optical fiber.20. The point light source according to claim 18, further comprising: athird laser for emitting a third light beam having a third wavelength;and a third optical fiber coupling the third light beam from the thirdlaser into the beam combiner, wherein the beam combiner combines thefirst, second, and third light beams, and wherein the first, second, andthird wavelengths are different from one another.
 21. The point lightsource according to claim 20, further comprising: a fourth laser foremitting a fourth light beam having a fourth wavelength; and a fourthoptical fiber coupling the fourth light beam from the fourth laser intothe beam combiner, wherein the beam combiner combines the first, second,third, and fourth light beams, and wherein the first, second, third, andfourth wavelengths are different from one another.